1. Filed of the Invention
The present invention relates to a construction of a face plate for a flat panel display such as a field emission display (FED), a plasma display panel (PDP), a liquid crystal display (LCD) and the like.
2. Related Background Art
In image displaying apparatus including CRT, larger surface construction has been sought and investigated vigorously. Further, as the large surface construction is achieved, it is important to make the apparatus thinner, lighter and less expensive.
However, in CRT, since electrons accelerated by high voltage are deflected by a deflection electrode to excite phosphor on a face plate, when the large surface is achieved, great depth is naturally required, with the result that is difficult to provide a thinner and lighter weight apparatus. The inventors have investigated a surface conducting type electron emitting element and an image displaying apparatus using such surface conducting type electron emitting elements as an image displaying apparatus capable of solving the above problem.
The Inventors have tried application of a multi electron beam source by using electrical wiring, as shown in FIG. 11, for example. That is to say, there has been provided a multi electron beam source in which a plurality of surface conducting type electron emitting elements are arranged two-dimensionally and these elements are wired in a simple matrix fashion as shown.
In FIG. 11, the reference numeral 4001 denotes the surface conducting type electron emitting elements schematically shown; 4002 indicates row direction wirings; and 4003 indicates column direction wirings.
Incidentally, for clarify""s sake, although 6xc3x976 matrix is shown, scale of the matrix is not limited to the illustrated one, but the number of elements sufficient to display a desired image may be wired.
FIG. 12 shows a construction of a cathode-ray tube using this multi electron beam source which includes outer container bottom 4005 and outer container frame 4007 having a multi electron beam source 4004, and a face plate 4006 having a phosphor layer 4008 and a metal back 4009. Further, high voltage is applied to the metal back 4009 of the face plate 4006 from a high voltage power supply 4010 through a high voltage introduction terminal 4011.
In the multi electron beam source in which the surface conducting type electron emitting elements are wired in a simple matrix fashion, in order to output a desired electron beam, an electrical signal is appropriately applied to the row direction wirings 4002 and the column direction wirings 4003.
For example, in order to drive the surface conducting type electron emitting elements in any one row of the matrix, selection voltage Vs is applied to the row direction wiring 4002 in the selected row, and at the same time, non-selection voltage Vns is applied to the row direction wirings 4002 in the non-selected rows. In synchronism with this, drive voltage Ve for outputting an electron beam is applied to the column direction wirings 4003.
According to this method, voltage (Vexe2x88x92Vs) is applied to the row direction wiring 4002 in the selected row and voltage (Vexe2x88x92Vns) is applied to the row direction wirings 4002 in the non-selected rows.
By selecting the voltages Ve, Vs, Vns to appropriate values, electron beams having desired intensity are emitted only from the surface conducting type electron emitting elements in the selected row, and, when different drive voltages Ve are applied to the respective column direction wirings, electron beams having different intensity are outputted from the elements in the selected row. Further, since a response speed of the surface conducting type electron emitting element is high, when a time period for applying the drive voltage Ve is changed, a time period for outputting the electron beam can also be changed.
The electron beam outputted from the multi electron beam source 4004 by the above-mentioned voltage application is illuminated onto the metal back 4009 to which high voltage Va is applied, thereby exiting and lighting the phosphor which is a target. Accordingly, for example, by appropriately applying voltage signals in accordance with image information, an image displaying apparatus can be obtained.
In such an image displaying apparatus, the multi electron beam source and the phosphor layer are formed within a glass vacuum container. Further, in many other image displaying apparatuses, a portion by which a picture plane is displayed is formed from a glass member.
If the image displaying portion of the image displaying apparatus is damaged, sharp glass pieces are scattered therearound, with the result that the observer may be in serious danger. Possibility of glass scattering is increased as the image displaying apparatus is made large-sized, and, thus, any means for preventing the glass scattering must be provided.
To this end, a technique in which a glass scattering preventing transparent film is adhered to a front surface of the face plate or a technique in which a transparent front plate made of acryl, polycarbonate or tempered glass is provided outside of the face plate have been proposed.
In the structure in which the glass scattering preventing transparent film is provided, when the voltage Va is applied to the inner surface of the face plate, the outer surface of the face plate and the transparent film are charged, with the result that uncomfortable discharging to the observer will occur or dust will be adhered to the transparent film to make it difficult to observe the picture plane. To avoid this, there has been a technique in which transparent electrodes are provided on the outer surface of the transparent film to form a charge preventing film which is grounded.
In the structure in which the transparent film having the charge preventing film is adhered to the face plate, the following problem occurs. That is to say, when the voltage Va is applied to the inner surface of the face plate and the outer surface of the transparent film is grounded, the face plate is subjected to voltage Vg smaller than Va.
Depending upon the glass used for the face plate, alkali ions (particularly, sodium ions) in the glass are shifted and precipitated and are reacted with moisture and/or carbon dioxide to form hydroxide and/or carbonate which colorize the glass surface to worsen the image quality of the image displaying apparatus.
To avoid this, although glass in which sodium ions are hard to be shifted can be used for the glass member of the face plate, such glass is not preferable since it is generally expensive to increase the entire cost of the apparatus.
The present invention aims to eliminate the above-mentioned conventional drawbacks, and an object of the present invention is to provide an image displaying apparatus in which shifting of ions in a face plate is suppressed by minimizing voltage to be applied to the face plate, thereby minimizing deterioration of image quality.
To achieve the above object, according to the present invention, there is provided an image displaying apparatus at least comprising a transparent film adhered to an outer surface of a face plate, and a transparent conductive film formed on an outer surface of the transparent film, and wherein, when there is potential difference between the transparent conductive film and an inner surface of the face plate, reduction in voltage of the transparent film becomes greater than reduction in voltage of the face plate.